1. Field of the Invention
The present invention relates to a three-dimensional measurement method and device for obtaining position information of an object by projecting light and receiving the light reflected from the object.
2. Description of the Related Art
Three-dimensional measurement can be accomplished using the time of flight (TOF) from the moment of light pulse transmission to the reception of the returning light pulse reflected by an object since this TOF is dependent on distance.
Japanese Laid-Open Patent Application No. H11-508371 discloses a device using a solid state area sensor as a photoreceptor device for modulating light entering the solid state area sensor by a photoelectric modulator. The distance is reflected in the amount of exposure light of the solid state area sensor by photoreception modulation synchronized with the projection light. The distance information to the object can be obtained regardless of the reflectivity of the object by determining the ratio of the amount of exposure light with modulation and the amount of exposure light without modulation. A measurement of distance to multiple points (so-called three-dimensional measurement or three-dimensional input) can be accomplished at higher speed using a solid state area sensor than which deflects the optical path by a scanning mechanism.
Japanese Laid-Open Patent Application NO. H10-332827 discloses a device for repeatedly projecting pulse light at uniform intervals, standardizing the amount of light of the reflected and returning pulse light which enters a solid state area sensor, and measuring the amount of light exposure in a specific period. The amount of exposure light is proportional to the frequency (number of pulses) of the reflected pulse light, such that the exposure light is slight when time-of-flight is long and the distance far. Three-dimensional input independent of the reflectivity of the object is possible by standardizing the amount of light of the reflected pulse light.
It is difficult to make a device compact since a light modulation device must be included in a construction for controlling the exposure timing of the solid state area sensor by light modulation as described above. In a construction for standardizing the amount of light of the reflected pulse light, disadvantages arise inasmuch as the allowed range of reflectivity of the object and the measurable distance range are limited by the performance of the optical system used for such standardization, such that resolution is determined by the period of the projection.
In the aforesaid conventional constructions, high-speed measurement at short distances is difficult because each uses a method of detection of the length of the time-of-flight based on the amount of exposure light.